Roadway repair is often accomplished by overlaying the existing pavement (whether of concrete or asphalt paving material) with a new layer (often called a leveling course) of concrete or asphalt paving material. This is an expensive and time-consuming process and is not always necessary. An alternative is to employ a chip sealing process for extending the useful life of the existing roadway. The typical cost of a chip sealing process is 20-25% of the cost of a conventional asphalt overlay. In the chip sealing process, a binder composition including asphalt cement is applied to the surface of the existing roadway, and then a layer of stone chips of high durability and high fracture plane characteristics is spread over the asphalt composition.
A chip seal is designed to seal and protect a pavement from oxidation and weathering by sealing the small cracks in a pavement surface and thereby preventing the intrusion of water into the pavement surface. A chip seal can also be used to address raveling (loss of aggregate), to correct bleeding and flushing problems, to improve skid resistance, and generally to extend the pavement life. Chip seals are not suited for all pavements; the existing structure should be sound with only minor surface defects. Consequently, chip seals are typically applied to pavements that are in relatively good condition with no structural damage. When a chip seal is applied to a pavement in good condition, an additional six to eight years of service may be expected. For more distressed pavements, less service extension can be expected (four to six years on pavements in fair condition and three to four years for pavements in poor condition).
Different types of asphalt cement binder compositions can be used in a chip sealing process. The composition may be applied with or without heating. Asphalt cement binder compositions that are applied without heating include modified and unmodified asphalt cement emulsions. Compositions that are applied hot can include polymer-modified asphalt cements, polymer-modified asphalt cements blended with rubber or crumb rubber, foamed asphalt cements and unmodified asphalt cements. The appropriate binder type is selected based on pavement condition, climate, aggregate properties, and desired service life and cost considerations.
In some conventional chip sealing processes, an emulsion is formed of asphalt cement and about 30% water. This emulsified mixture is then applied to the road using an emulsion supply truck equipped with a spray assembly. As soon as the asphalt cement emulsion meets the road surface, the water in the emulsion begins to evaporate. Consequently, it is necessary to apply a layer of stone chips to the roadway immediately after the application of the asphalt cement emulsion.
However, the chips must be applied to the roadway surface without having the wheels of a vehicle drive on the chip-free emulsion on the roadway surface.
A conventional chip spreader is a self-propelled vehicle that has a hitch assembly on its rear end for coupling it to the rear end of a chip supply dump truck. The chip spreader has a receiving hopper on its rear end that is adapted to receive chips when the dump bed of the supply truck is raised. However, the receiving hopper can only accommodate a portion of the load of the supply truck, so the chip spreader will pull the chip supply dump truck backwards as chips are conveyed from the receiving hopper to a chip spreader assembly on the front end of the chip spreader. The driver of the chip supply dump truck is required to steer the vehicle as it is being pulled backwards by the chip spreader. This can be difficult, especially since the driver is facing away from the direction of travel and his vision in the direction of travel (i.e., that obtained by turning his head around or using mirrors) is partially blocked by the raised dump bed.
It would be desirable if a chip sealing method and apparatus could be developed that would permit chip sealing to be carried out without requiring the chip supply dump truck to travel backwards during the chip sealing process.